With more Spotify-like services on the horizon, a bounty of unexplored music beckons. But will they do a better job of helping you figure out what to listen to next?

AS A WALL STREET Journal entertainment reporter, I have an enviable music supply. My desk is piled with promotional CDs; links to download unreleased albums flow into my inbox daily; and going to concerts is part of the job description. I'm steeped in new music—so why would I draw a blank when trying to figure out what to listen to on my evening train ride home? Confronted by the empty search bar on Spotify, I sometimes feel paralyzed. The unseen presence of the app's 20 million songs weighs down on me with each flash of the...